The reason to reconfirm flights to be aware of any last-minute schedule changes that may have occured whilst you were travelling and the airline would have to way to reach you. If they move the flight up and you miss it, they may say that you are responsible for not re-confirming. I had a flight routing change on the way back from Rome and without reconfirming, I would have been mighty confused, as that airport lines up by flight number rather than having a general airline counter.